1. Field of the Invention
The present invention relates to a method for individually fitting a hearing instrument.
2. Description of Related Art
A hearing instrument usually comprises a microphone for generating an input audio signal from ambient sound, an audio signal processing unit (which nowadays often is digital) for processing the input audio signal into a processed output audio signal and an output transducer for stimulation of the user's hearing according to the processed output audio signals. Audio signal processing in the audio signal processing unit involves applying a gain function to the input audio signal, which depends on level and frequency of the input audio signal. Hearing instruments usually are used by persons suffering from a hearing loss compared to normal-hearing persons, which depends on level and frequency of the ambient sound. Usually the hearing instrument undergoes a fitting procedure in order to individually set the gain provided by the hearing instrument such that the hearing loss of the user is compensated as far as possible.
In the prior art various attempts have been made for the fitting of hearing aids to the needs of an individual patient.
U.S. Pat. No. 4,577,641 relates to a fitting process for a cochlear implant wherein equal loudness contour (ELC) measurements are conducted after the device has been implanted in order to determine the individual optimized gain function of the hearing instrument. The ELC measurements are carried out at the most comfortable loudness level.
U.S. Pat. No. 4,471,171 relates to a hearing instrument with an electroacoustic output transducer, wherein a sound generator is integrated within the hearing instrument for performing hearing threshold measurements as a function of frequency.
U.S. Pat. No. 6,788,790 relates to the integration of a sound generator for audiometric measurement within a partially or fully implantable hearing instrument for e.g. direct mechanical stimulation of the inner ear.
According to EP 0 535 425 B1 loudness curves as a function of the sound input level are measured for various frequencies. From these loudness curves contours of equal loudness as a function of frequency are plotted for various loudness values. However, the loudness curves are obtained without the hearing aid being used.
US 2002/026091 A1 relates to an implanted hearing instrument with an electromechanical transducer, wherein the quality of the coupling between the transducer and the user's ear is evaluated by measuring the mechanical impedance after implantation of the transducer.
EP 0 661 905 B1 relates to a fitting model for hearing aids in order to take into account various psycho-acoustic effects, i.e. in order to take into account the fact that loudness curves are measured with sinus tones or low-band noise while practical ambient sound, in particular speech, is perceived by the user in a much more complex manner than sinus tones or narrow-band noise.
Fitting procedures for hearing instruments with electroacoustic output transducers are suggested in U.S. Pat. No. 6,574,342 B1 and U.S. Pat. No. 6,201,875 B1 which propose to perform measurements of the contours of equal loudness with the hearing instrument worn by the user and with the stimuli created by the hearing instrument itself. In these measurements, for a plurality of frequencies f or frequency bands, the input level of the hearing instrument is varied such that the loudness perceived by the user is kept constant. This procedure is repeated for different values/categories of loudness ranging from very soft to extremely loud. The thus measured contours of equal loudness are used to determine the individual gain function which is finally implemented in the hearing instrument to compensate for the user's individual hearing loss.
While using the fitting procedures suggested in U.S. Pat. No. 6,574,342 B1 and U.S. Pat. No. 6,201,875 B1 the hearing device can be well fitted to the individual hearing loss experienced by the patient, these procedures are disadvantageous in that a large number of measurements has to be taken. In particular, in the fitting procedures described in U.S. Pat. No. 6,574,342 B1 and U.S. Pat. No. 6,201,875 B1 measurements are taken at 12 different frequencies for 7 different loudness levels. That means that 84 individual reading points are investigated, which necessitates a lengthy and troublesome procedure both for the patient and the physician or audiologist.
It is an object of the invention to provide for a simple and nevertheless accurate method for individually fitting a hearing instrument comprising an output transducer for stimulation of the human auditory system.
These and further objects, features and advantages of the present invention will become apparent from the following description when taken in connection with the accompanying drawings which, for purposes of illustration only, show several embodiments in accordance with the present invention.